This article presents a study investigating musical learning among 9th grade adolescents in a Swedish lower secondary school. The adolescents collaboratively composed songs for a self-written musical, which they taught to their peers. The purpose of the study was to explore the ways in which adolescents acquire musical knowledge in this specific setting. A sociocultural perspective was employed, and the methods used were observations and interviews with the adolescents. The results demonstrated that the adolescents' choice of tools when learning and teaching their peers were the same as those used by their teacher. The written score was distinct in all their musical learning, suggesting the dominance of the written paradigm. In conclusion, in order to support musical learning, music teachers need to know how to create opportunities for peer teaching and leaving the students to themselves, and when to interfere and guide the adolescents into their Zone of Proximal Development.